The following description of the background of the invention is provided to aid in understanding the invention, but is not admitted to be, or to describe, prior art to the invention. All publications are incorporated by reference in their entirety.
The presence of arsenic and other toxic metals in ground water and other sources of water is an environmental concern. These toxic metals occur in groundwater, water sources and soil both naturally and as contaminants from various sources including but not limited to sources such as industrial wastes, byproducts of manufacturing, agricultural wastes and byproducts. A method of stabilizing mercury and other heavy metals in particulate material, such as sludge, is described by Broderick et. al. in US 200/0106317A1. The described method uses a metal reagent in addition to sulfur-containing compound and proposes agitating these materials plus others in an oxygen atmosphere. In this process the excess sulfides that were added to remove the metals have to be removed also as they become contaminates.
There are known methods for removing arsenic and other toxic metals from ground water and contaminated water which differ slightly for each metal contaminant. As an example, one method for arsenic involves the reduction of arsenic to the arsenite form and then complexation by resins, clays, carbon or zeolites. When the arsenic is trapped in such filtration systems, the complexing system must be removed along with the entrapped arsenic. These systems have not proven very useful for use in aquifers due to the mechanical complexities. Sulfhydrated cellulose (Lindahl et. al., WO8802738) was used in a bed as an ion exchange treatment to adsorb mercury, cadmium, and lead from solutions. The filter material was then stripped with aqueous 1M or greater HCl for conventional precipitation as sulfides. There have been similar other applications of the ion exchange technique (Furuta et. al, EP352420; Yan, U.S. Pat. No. 4,915,818) to remove metals from liquid hydrocarbons. However these methods are not useful to remediate water in situ.
Zero valent iron has been proposed to treat groundwater and surface streams for decontamination (Ponder et. al, US 20020006867A1 and U.S. Pat. No. 6,242,663). Another presently used common technique for decontaminating aquifers is the pump-and-treat method. This method utilizes a series of extraction wells drilled into a contaminated aquifer. The contaminated water is drawn through an extraction well, treated to remove or degrade the contaminant, and then returned to the aquifer through one or more injection wells or discharged to sewers or other non-origin points. This method can be both time consuming and cost-prohibitive
A treatment method for arsenic in water with proteins derived from microbes that routinely process arsenic via metabolic process has been suggested by some. This presently appears to be a process that is too expensive to have practical application for bioremediation. Although a large number of genetic studies have been done on microbes that can process As or other metals (e.g. Hg), the basic problem for the use of any of the microbes with metals is to devise a relatively inexpensive means of reducing the contaminating metals with the microbes and then binding the reduced metals to a substrate.
The approach of growing organisms to extract the polypeptides or synthesizing complex polypeptides is costly. Growing organisms for extraction of products from the organisms is viable when the value of the extracted products, such as pharmaceuticals, is expected to be high. However, in the case of treating soil and water contamination, large volumes must be treated over extended periods and cost has proven to be a limiting factor.
All of the previously mentioned methods have shown serious shortcomings. Addition of complexing materials has the problem that essentially all of the materials is released at once. Thus, frequent addition of the chosen material is needed to keep a sufficient concentration in the contaminated area over time. The constant injection of high volumes of solutions will increase the volume of the system or aquifer and thereby potentially cause further spread of the contamination. Special measures are required to deoxygenate the water and solutions which are injected, to ensure maintaining the anaerobic atmosphere which fosters the reduction. Thus a need exists for a safe, cost-effective method for removing these contaminating materials from ground water and soils.